[Bug 98472] New: [i965][SKL] External display blanks intermittently with Skylake in Linux 4.9rc2

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98472

            Bug ID: 98472
           Summary: [i965][SKL] External display blanks intermittently
                    with Skylake in Linux 4.9rc2
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: brettcsmith at brettcsmith.org
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

I previously chimed in on #97450.  That's been marked resolved as of Linux 4.9,
but my issue remains, so I'm filing this as a separate bug.  If it's actually
the same, it's fine by me to close this as duplicate and reopen #97450.

I have a Dell XPS 13 9350.  I usually connect to an external Philips 288P6LJEB
with a USB-C to DisplayPort cable, running 3840x2160 at 60.0Hz.  The monitor is
configured to use DisplayPort 2.0.  I'm primarily running Debian stable
(jessie), with the following installed from backports:

firmware-amd-graphics 20160824-1~bpo8+1
irqbalance 1.1.0-2~bpo8+1
iucode-tool 2.0-1~bpo8+1
libdrm-amdgpu1:amd64 2.4.71-1~bpo8+1
libdrm-intel1:amd64 2.4.71-1~bpo8+1
libdrm-nouveau2:amd64 2.4.71-1~bpo8+1
libdrm-radeon1:amd64 2.4.71-1~bpo8+1
libdrm2:amd64 2.4.71-1~bpo8+1
libegl1-mesa:amd64 12.0.3-1~bpo8+1
libegl1-mesa-drivers:amd64 12.0.3-1~bpo8+1
libgl1-mesa-dri:amd64 12.0.3-1~bpo8+1
libgl1-mesa-glx:amd64 12.0.3-1~bpo8+1
libglapi-mesa:amd64 12.0.3-1~bpo8+1
libvdpau1:amd64 1.1.1-1~bpo8+1
linux-base 4.3~bpo8+1
mesa-vdpau-drivers:amd64 12.0.3-1~bpo8+1
xserver-xorg-video-intel 2:2.99.917+git20160706-1~bpo8+1

Intermittently, the monitor will go blank for about 3 seconds.  It's hard for
me to say how much of this is the software, versus how much is the monitor: in
general, this monitor is slow to wake up (both during power up and coming back
from sleep), so it's possible that the original event is very brief and then it
takes the monitor a couple of seconds to adjust back to where it should be.

No messages from Linux correspond to these events.  However, the resolution
does get re-reported in Xorg.log:

[  2216.405] (--) intel(0): HDMI max TMDS frequency 600000KHz
[  2216.412] (II) intel(0): resizing framebuffer to 3840x2160
[  2216.460] (II) intel(0): switch to mode 3840x2160 at 60.0 on DP1 using pipe 0,
position (0, 0), rotation normal, reflection none
[  2217.663] (--) intel(0): HDMI max TMDS frequency 600000KHz
[  2219.749] (II) intel(0): resizing framebuffer to 3200x1800
[  2219.750] (II) intel(0): switch to mode 3200x1800 at 60.0 on eDP1 using pipe 0,
position (0, 0), rotation normal, reflection none
[  2220.431] (--) intel(0): HDMI max TMDS frequency 600000KHz
[  2220.439] (II) intel(0): resizing framebuffer to 3840x2160
[  2220.454] (II) intel(0): switch to mode 3840x2160 at 60.0 on DP1 using pipe 0,
position (0, 0), rotation normal, reflection none
[  2221.660] (--) intel(0): HDMI max TMDS frequency 600000KHz
[  2532.187] (II) intel(0): resizing framebuffer to 3200x1800
[  2532.189] (II) intel(0): switch to mode 3200x1800 at 60.0 on eDP1 using pipe 0,
position (0, 0), rotation normal, reflection none
[  2547.231] (--) intel(0): HDMI max TMDS frequency 600000KHz
[  2547.242] (II) intel(0): resizing framebuffer to 3840x2160
[  2547.270] (II) intel(0): switch to mode 3840x2160 at 60.0 on DP1 using pipe 0,
position (0, 0), rotation normal, reflection none
[  2549.206] (II) intel(0): resizing framebuffer to 3200x1800
[  2549.209] (II) intel(0): switch to mode 3200x1800 at 60.0 on eDP1 using pipe 0,
position (0, 0), rotation normal, reflection none
[  2559.262] (--) intel(0): HDMI max TMDS frequency 600000KHz
[  2559.278] (II) intel(0): resizing framebuffer to 3840x2160
[  2559.300] (II) intel(0): switch to mode 3840x2160 at 60.0 on DP1 using pipe 0,
position (0, 0), rotation normal, reflection none
[  2560.521] (--) intel(0): HDMI max TMDS frequency 600000KHz

DP1 is the laptop's own display, which is turned off (through GNOME
configuration) when I'm connected to the monitor.  The reported resolution
always looks correct and unchanging, so I'm not sure what it means that the
framebuffer is being "resized."

I have seen this issue on every version of Linux I've tried: 4.6 and 4.7
installed from Debian backports, every version of 4.8 built from source, and
now 4.9rc2.

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